Electric circuit breaker



Jan. 15, 1946. 'L. s. HOBSON ELECTRIC CIRCUIT BREAKER Filed Feb. 27, 1943 Inventor: Leland '5. Hobson, by WM 524441.4

His Attorney.

Patented Jam-15, 1946 UNITED STATES PATENT OFFICE ELECTRIC CIRCUIT BREAKER I Leland S. Robson, .Drexel Hill, Pa, asslgnor to General Electric Company, a corporation of New York Application February 27, 1943, Serial No. 477,377

4 Claims. (Clf200-144) My invention relates to electric circuit breakers, more particularly to air circuit breakers of the magnetic blowout type for interrupting moderate voltage power circuits, and has=for its principal object the provision of an improved air circuit breaker of the aforesaid type that embodies the interleaving barrier principle of arc extinction that is compact and simple in construction for a given interrupting rating and that is also adapted efllciently to dissipate and disperse the I highly heated gases expelled incident to are interruption from the arc chamber or chute so as to lessen greatly the likelihood of flash-over, or restriking of the are, at thechute exhaust.

The use of magnetic blowout air circuit breakers comparable in size to oil circuit breakers for interrupting power circuits at distribution voltages, such as 5000 volts, has been made possible by improved arc chute construction. In one well known form of magnetic blowout air circuit breaker, the arc is greatly lengthened and attenuated within the arc chute and cooled throughout its length. This results in a rapid increase of the arc stream resistance so that the current is correspondingly decreased and the power factor greatly improved thereby facilitating interruption at a current zero. However, it has been found in the case of heavy overload and short circuit currents that the highly heated arc gases expelled from the chute sometimes form a conducting path through which the arc may restrike after it has been interrupted within the chute. Such restriking or flash-over at the chute exhaust usually results in failure of the breaker to clear the circuit and damage to other equipment may result therefrom. It has also been. found desirable further to lengthen the are by additional looping thereof between interleaving bafile or barrier structure.

In accordance with my invention, the chute is designed so that there is wide dispersal and dis sipation, tending toward rapid cooling, of the arc exhaust gases without sacrificing compactness and the benefits of even greater are lengthening and attenuation within the chute itself.

My invention will be more fully set forth in the following description referring to the ac-' companying drawing, and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

Referring to the drawing, Fig. 1 is an elevational view, partly in section, of an air circuit breaker of the magnetic blowout type embodying my invention; Fig. 2 is a partly sectional end view part of the present invention, a' complete disclosure thereof is omitted in the interest of clearness.

The circuit interrupter comprises essentially means for opening the circuit to form the interrupting arc, and are extinguishing structure. Specifically, the circuit opening means comprises a relatively fixed contact 1 and a movable contact 2 that is pivotally mounted at 3 on one of the circuit breaker studs and is operated by means of a reciprocally movable rod 4. The operating rod is suitably connected to an actuating mechanism (not shown) for operating the movable contact between closed and open circuit positions. The contacts I and 2 are electrically connected to the lower ends of the breaker leadin conductor studs 5 and 6 respectively which also serve as the breaker terminals. Accordingly,

when the breaker is connected in series in a power circuit and the contacts I and 2 are separated, an arc may form across the gap indicated.

For the purpose of interrupting this power arc, an arc extinguishing structure, such as the arc chute, generally indicated at l is mounted with respect to the contact structure so as directly to receive the power arc which is under the influence of the magnetic blowout fields produced by the coils 8 and 9. The switch contacts and the magnetic blowout structures can assume any preferred form and comprise no part of the present invention so that a brief description will be sulficient. Two magnetic blowout coils. 8 (but one is shown) are electrically connected to the conductor stud 5 and to the conducting are runners 8' so that the arc current (as the arc travels along the runners) flows through the blowout coils, as well known in the art.

Normally the current is carried in the closed circuit position of the breaker by the spring biased contact i, the current being shunted to the arcing contact at l upon opening of the breaker. As the arc is drawn by the movable contact 2, it is transferred to the arc runner 9' when it passes the position indicated by Fig. 1

manner at the outer opposite sides of the arc chute.

The are chute l is designed for interrupting the are, preferably by lengthening and attenuating it within restricted insulating passages so that the resistance of the arc stream is progressively and greatly increased, as described in Letters Patent 2,293,513, issued August 18, 1942, to L. J. Linde for Electric air circuit breaker. As illustrated by Fig. 1, the arc extinguishing structure according to the present invention is formed as a chute by closely spaced side walls 10 and I i composed of arc resisting material such as, for example, an asbestos compound or a suitable arc resisting ceramic material. Each side wall of the chute is fan-shaped, as shown, and at its inner side facing the other wall is provided with a plurality of arc baffles, such as rib-like fins or ridges indicated at HM and Ho. The ridges extend radially from the contact end of the chute and are preferably integral with the chute side Walls which are in turn suitably joined and clamped together as halves of the chute. The height and spacing of the ridges, as illustrated by Fig. 3, are such that when the side walls are clamped together, the ridges are interleaved (Fig. 2) in spaced relation with respect to each other, i. e., in staggered relation, so as to form a restricted zigzag passage having alternating salients into which the arc is driven from the entrance 12 of the arc chute.

As clearly shown by Fig. l, which illustrates but half the are chute in detail, namely, the side wall i i, the ridges extend longitudinally in spaced radial or diverging relation from the chute entrance to the chute exhaust, so that the salient height of the ridges is in a direction transverse to the direction of movement of the arc as it moves through the chute. For the purpose of properly confining and attenuating the arc near the chute exhaust where the ridges are more widely spaced, I provide 2. tier of short or stub ridges 10b and lib between the main ridges Ilia and Ho, respectively, of the corresponding chute sides. As shown by Fig. 1, two stub ridges are located between the upper diverging ends of each pair of main ridges and these stub ridges extend only part way toward the contact or entrance end of the chute thereby providing adequate space between the converging ends of the main ridges at [2 for free passage of the arc into the chute. It will therefore be seen that the length of the zigzag path for the arc is greatly increased toward the exhaust end of the chute, not only by the fan shape of the chute but in greater degree by the additional looping of the are by the stub ridges.

Therefore, as the arc is driven by the blowout field into the zigzag space defined by the interleaving ridges, the cross-section of the arc is reduced as the arc more and more assumes a serpentine form. If a heavy current are is to be interrupted, interruption may not occur until the arc has been moved well into the chute. Up

to the point or interruption, the blowout field continues to move the arc outward through the arc passage, thereby progressively lengthening the path 01' the are as the amplitude of the zigzag path becomes greater. The are is thereby greatly lengthened and attenuated concurrent with very effective cooling as it approaches the exhaust part of the chute due mainly to the large cooling surfaces of both the main and stub ridges. It will also be seen that the radially disposed baiiles and fan-shaped chute provide at the elongated chute exhaust increased voltage striking length, thereby reducing the potential gradient and minimizing the danger of flash-over, or restriking of the arc, across the chute exhaust.

For the purpose of retarding or throttling'the movement 0! large current arcs within the chute and for cooling and providing adequate venting area for the arc gases, I provide means disposed at the chute exhaust for restricting or decreasing the venting area. This restriction of the venting area also materially reduces the likelihood of flame-throw from the chute.

In the aforesaid Letters Patent to Linda there is illustrated a muffler for suppressing and confining within the chute heavy overload or short circuit arcs. In this arrangement, the grid-like structure of the muiiler also freely vents arc gases generated within the chute, the above-described zigzag arc passage simply opening into the muiller at the chute exhaust. My invention is not limited to a specific form of muffler and by way of example there is shown a curvilinear grid-like cooling and venting arrangement comprising spaced insulating fibre plates I3 disposed between the chute sides edgewlse with respect to the flow of exhaust gases and transverse with respect to the general length of the are between terminals. Between the fibre plates are located metal screens or gauze H, preferably of good heat conductivity. Forming a part of the muiiler is an insulating wedge member l5 composed of hard fibre extending entirely across the exhaust end of the chute at the mid-section thereof, as shown by Fig. 2. This member also extends into the chute to a point adjacent to the ends of a pair of stub ridges, as illustrated by Fig. 1, thereby dividing and deflecting in opposite directions the mass of hot gases expelled from the chute and muilier.

This division, deflection and dissipation of the arc gases is furthermore greatly augmented by the radial arrangement of the main and stub ridges and by the fan shape of the chute whereby the gases are vented along practically a semicircle of arc. This greater length along the chute exhaust materially increases the effective muiller area and also provides a longer line of contact between the muiiler and the end of the chute. As previously pointed out, it. is advantageous to have this greater length for reducing the potential gradient so as to reduce the danger of flashover along this line.

It will thus be noted that the gases are discharged from the chute in widely diverging directions so that they are largely diffused and dissipated instead of concentrating at the exhaust for causing flash-over.

Although I have shown but two tiers of chute ridges, i. e., the main ridges Illa and I la and the stub ridges lllb and ilb, it should be understood that more than two tiers ma be used if desired depending on the size of the chute used, the main consideration being to squeeze and attenuate the arc up to the very exhaust end of the chute.

aseaies Otherwise, the interleaving eilicieney of the chute would be comparatively poor because wide spaces between the outer ends of the ridges indicate that a large proportion of the chute section is taken up by an arc path component parallel to the sides 01' the chute and therefore of no interleaving value.

It should be understood that my invention is not limited to specific details of construction and arrangement thereof herein illustrated, and that changes and modifications may occur to one skilled in the art without departing from the spirit or my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electric air circuit breaker comprising contacts separable to form an interrupting are, a tan-shaped arc chute into which said are is directed, said chute having an approximately semicircular exhaust opening for venting arc gases generated within said chute, interleaving arc bai'lles formed wholly oi insulating material disposed within said chute extending radially from the arc entrance portion of the chute to iorm a zigzag path for a single arc and to vent said are gases in diverging directions radially from the exhaust opening, and interleaving stub baiiies also formed wholly of insulating material arranged between said first-named baiiles at the exhaust opening of said chute materially to increase the number of loops of said zigzag path for said single are at said exhaust opening as contrasted with the number of loops of said zigzag path for said single are near the entrance portion of said are extinguishing structure.

2. An electric air circuit breaker or the magnetic blowout type comprising contacts separable to form an interrupting are, an arc chute into 7 which said are is directed, said chute having a substantially semi-circular exhaust opening for venting arc gases generated within said chute tier at said exhaust opening, and additional interleaving baflies formed wholly of insulating material arranged in a tier between said first-named baii'ies and adjacent to said muiiier materially to increase the number or loops of said zigzag path at said exhaust opening as contrasted with the number of loops of said zigzag path near the entrance portion or said arc extinguishing structure, said additional baiiles being materially shorter than said first-named baiiles and more than one additional bailie being provided between each pair or said first-named baiiles.

3. An air circuit breaker comprising an arc chute having an arc entrance portion and a curvilinear exhaust opening i'or venting arc gases from said chute, relatively movable contacts separable at said entrance portion, radially disposed interleaving arc baiiies extending tan-wise from said entrance portion toward said curvilinear exhaust opening for interrupting and extending a single arc and dividing and diverting the ilow of are gases from said chute in widely divergent directions, and additional are baiiles formed wholly of insulating material disposed adjacent to said exsaid entrance portion, radially disposed interleaving arc baiiies extending fan-wise from said entrance portion toward said exhaust opening for interrupting and extending a single arc and dividing and diverting the flow of are gases from said chute in widely divergent directions, and additionai arc baiiles formed wholly of insulating material disposed adjacent to said exhaust opening and materially shorter than said first-named baiiles, all of said bailles extending substantially to said exhaust opening.

LELAND S. HOBSON. 

